Error handling without creating parallel branch

[drmrbrewer]

My flow is currently as follows:

I am catching an error in the "get metadata" step (can't find file) using a "Configure run after", and if there is an error all I'm doing at  the moment is terminating with "cancelled" status.

This works fine, but it irritates me from a layout point of view that I've doubled the width of my flow just to create a single "terminate" step.

What I would prefer is a way to wrap the "get metadata" step in a try/catch type block, so the error handling sits "in line" with the rest of the flow... after all, I'm only terminating on error, nothing fancy.

Is this possible?

And yes, I know that my parallel branch isn't strictly necessary in this context because the flow will terminate anyway, but I'd rather it terminates with "cancelled" than "failed" here, because it is expected that this file won't be present in many cases... so it's not a failure as such.

Perhaps it would be better to handle this with a condition on the trigger, so that the flow doesn't run at all in those circumstances.  But I'm not sure if it's possible for a condition to check for the existance of a file?  And anyway I'm still interested to know whether a try/catch approach is possible.

[Nived_Nambiar · Accepted solution]

Hi @drmrbrewer 

First let's discuss a basic try catch- final block how it can be created in the power automate flow 

See below

First step is to create a variable which stores whether error occured or not, it would be a boolean variable , so initially we would assign it as true (as seen in above screenshot)

Next for the purposes of showing how should Try catch final block should be designed, i am demonstrating with scope actions where we can group multiple actions together, you can even go for single action for try section and scope for catch and final section (as per your wish !)

Try Scope

Place the actions you need to run in try scope

Catch Scope

Catch scope captures all exceptions when try scope fails 

Configure run after should be set as 

It should run when try scope is failed/timed out.

Final Scope

Final scope should run even everything is success or any failure so best point where you can terminate your flow would be here.

Configure Run after should be set as 

Hope this helps !

Also regarding the trigger to check for existence of file, i see you are triggering the flow when the file is created , i assume you are trying to fetch the proeprties of same file, if yes it should not throw error right?

Also the action you are using Get File Metadata using path instead of that try to use get file metadata and pass the ID dynamic content which you got as output from the trigger in File Identifier field.

Thanks & Regards,

Nived N 🚀

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[drmrbrewer]

@Nived_Nambiar thanks for the reply, I'll check out your try/catch suggestion, it looks neater than my flow.  Question though: I need the flow to continue after the try/catch/final blocks, assuming that the try didn't end up in catch/final... will that be the case here?

Regarding:

> Also regarding the trigger to check for existence of file, i see you are triggering the flow when the

> file is created , i assume you are trying to fetch the proeprties of same file, if yes it should not

> throw error right?

I am checking for any new file e.g. "my_file.txt" and then reading some metadata from a file with the same name but .json extension e.g. "my_file.json".  Actually, to ensure uniqueness, I am just adding the .json after the full name including extension e.g. "my_file.txt.json" (in case there is "my_file.txt" and "my_file.docx").

But not all new files will have an associated .json file (and that's expected and normal).

So ideally, I don't want to trigger the action and then fail/cancel it if there is no .json file... but it would be far cleaner to not trigger at all in the first place (if there is no json file).

[Nived_Nambiar]

Hi @drmrbrewer 

You can place actions after final block to run if try is executed successfully, but make sure that to use that error boolean variable so that you can run the flow only when there is no error (or that error variable is false)

There is no action which checks the existence of file, but one way you can try is 

1. List all files in folder

2. use filter array to filter for the file name, if file exists, then no such json file exists and you can configure flow accordingly.

Thanks & Regards,

Nived N 🚀

LinkedIn: Nived N's LinkedIn
YouTube: Nived N's YouTube Channel

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[drmrbrewer]

@Nived_Nambiar 

> You can place actions after final block to run if try is executed successfully, but make sure that to

> use that error boolean variable so that you can run the flow only when there is no error

> (or that error variable is false)

Though presumably if my catch block is already doing a Terminate on error, there is no need to check the variable again after the final block?

> There is no action which checks the existence of file, but one way you can try is

I can already check for the existence of the file using an action (that is what the Get File Metadata action is doing... it gets the ID but also errors out if the file does not exist... hence allowing me to use this to check for existence). 

The question I have now is not how to use an action to check for file existence, but whether I can use a condition of the trigger itself... it's better that the flow does not trigger at all if there is no metadata file (vs triggering and then failing after triggering).

[FLMike]

Hi,

Yes you can add a filter on the Trigger itself. I am not sure what the metadata file is so I cannot exactly tell you what the filter should look like, as the trigger condition can be just about anything.

Click ... of the Trigger

Go to Settings

Add a trigger such as 

@equals(triggerBody()?['{FilenameWithExtension}'],'my meta data file')

In your case, whatever your doing in the Get meta data file, you need to turn that into a condition check as a file a such bla bla bla is NULL or empty or some name etc

Cheers
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Michael Gernaey MCT | MCSE | MCP | Self-Contractor| Ex-Microsoft
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[drmrbrewer]

@FLMike thanks.  It's not quite what I mean.  Let me explain more...

At the moment, I'm triggering on any new file, with any name.  Some of those might have an associated .json metadata file (with same base name).  So the .json metadata file doesn't have a fixed name... it is based on the associated file. 

So I might create new file "myfile.txt" with associated "myfile.txt.json" (same name but with a .json extension).  I trigger on any non-json file (could be .txt .pdf .docx ... anything)... that is the file I want to work on.  Then I check if there's a corresponding .json file, and use that to update metadata of the main file.

So the condition on the trigger needs to be "only trigger from this file if there another file in the same folder with the same name as this file but with an extra .json".

[FLMike]

Yeah that's totally possible. And I got it before, thought I was clear you needed to write what would work for you apologies if somehow it was not.

If you want the filter to get the incoming name, change the extension to .json and validate it exists.. you can.

And if nothing else, you could have added a condition to check it initially, but you would have had to paths, just like in catching that an error occurred in a parallel branch. You would have had Yes and No condition branch.

Whatever works for you works for me 🙂

Cheers
If you like my answer, please Mark it as Resolved, and give it a thumbs up, so it can help others
Thank You
Michael Gernaey MCT | MCSE | MCP | Self-Contractor| Ex-Microsoft
https://gernaeysoftware.com
LinkedIn: https://www.linkedin.com/in/michaelgernaey

[drmrbrewer]

@FLMike 

> If you want the filter to get the incoming name, change the extension to .json and validate it exists.. you can.

How do you validate that another file exists in the Trigger Condition?

[Nived_Nambiar]

Hi @drmrbrewer 

I think you need to check for json file only when the file of other extension is created, for that follow this approach.

First use trigger to trigger when non json files are added to a specific folder , for making it trigger only when non json files are added, use the below trigger condition in trigger

@equals(not(endsWith(triggerOutputs()?['body/{FilenameWithExtension}'],'.json')),true)

Next use Get files to get the details of all files in folder, you can point this action for the folder location where json file will be created.

Also use filter query to check for the files having name equals Name of file created by trigger.json , like below

The output of above action would be list of values which satisifies the filter condition, if output has no values, then it means there is no json file corresponding to the created file, else there is a json file corresponding to that of file

Expression used to evaluate the whether the output of get files has values or not:

length(outputs('Get_files_(properties_only)')?['body/value'])

In Yes branch: do actions when json file not exists

in No branch: do action when json file exists 

Hope it helps !

Thanks & Regards,

Nived N 🚀

LinkedIn: Nived N's LinkedIn
YouTube: Nived N's YouTube Channel

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[drmrbrewer]

@Nived_Nambiar it's still not what I mean.  I don't know how else to explain it.  I already know how to use an action to check whether the json file exists... see my original flow which already does it.  But that check happens after the flow has been triggered.  I'm trying to avoid the flow triggering at all, if the json file does not exist... i.e. using a trigger condition not an action.  Never mind, you answered my original question re try/catch and that's working nicely, thanks.

FWIW I think I'm going about this the wrong way round.  At the moment I trigger on creation of a non-json file (this is the file I'm really interested in, to update properties of that file) and then check if there's a corresponding json file (bailing out if not).  I think it would be better to trigger on creation of the json file instead, and check if the corresponding file exists (the file being specified in the json).  That way, I'm only triggering when there is a json, and perhaps only in a specific folder... this will limit the flows that are triggered.